DEVELOPMENT OF THE MEMBERS OF A BRANCH-SYSTEM. 187 
which lateral shoot when we have sympodial pseud-axes. Sometimes, however, distor- 
tions occur {e.g. in Solanaceae) which might lead to erroneous conclusions if reference 
were not made to the earliest stages of development. 
Sect. 26. The Relative Positions of Lateral Members on a Common 
Axis^ — In order to bring the facts which we have now to consider into a clear 
and simple arrangement, it is necessary, in the first place, to explain the use of a 
few technical expressions and geometrical modes of representation. 
By the term Axial Structm-e or Axis is to be understood, in future, when the 
contrary is not expressly stated, any member that continues to grow at its apex 
and produces lateral members ; for example, a mother-root with its lateral roots, 
a stem with its leaves ^, the mid-rib 
of a leaf with its leaflets, pinnae, 
or lobes, or a thallus-shoot with its 
lateral outgrowths. 
If two or more similar lateral 
members proceed in different direc- 
tions from the same transverse zone 
of an axis, they constitute a Whorl. 
A true whorl results when the zone 
of the axis which produces it is 
always at right angles to the axis 
(Fig. 136); a Spurious or Pseudo- 
Whorl when the zone is the result 
of unequal development of the axis, 
or when lateral members which 
were formed at the same level 
have become so far separated by 
subsequent unequal elongation of 
the axis, that they appear, in the 
mature state, distributed into different 
zones. Siinulianeous Whorls are those 
whose members are formed simul- 
taneously (Fig. 144). Whorls are 
successive when the members at the 
same zone grow in succession either 
right and left, as is shown in Fig 145, and as occurs in the true leaf-whorls of 
^ Roper, Linnsea, 1827, p. 84, — Schimper-Braun, Flora, 1835, pp. 145, 737, 748. — Bravais, 
Ann. des Sei. Nat., vol. VII. 1837, pp. 42. I93- — Wichura, Flora, 1844, p. 161. — Sendtner, Flora, 
1847, pp. 201, 217. — Brongniart, Flora, 1849, p. 25. — Braun, Jahrb. für vi'issen. Bot. vol. I. 1858, p. 
307. — Irmiscli, Flora, 1851, pp. 81, 497. — Hanstein, Flora, 1857, P- A^l' — Schimper, ditto, p. 680. — ■ 
Buchenau, Flora, i860, p. 448. — Stenzel, Flora, i860, p. 45. — Numerous papers by Wydler, e. g. 
Linnsea, 1843, p. 153; Flora, 1844, 1850, 1851, 1857, 1859, i860, 1863, and elsewhere. — Hofmeister, 
Allgemeine Morphologie der Gewebe, §§ 8, 9. [Haughton, Manual of Geology. — Elbs, Mathe- 
matical Tracts. — A. Dickson, Trans. Royal Soc. Edinb. vol. XXVI. p. 505. — Chauncey Wright, 
Mem. Amer. Acad. vol. IX. p. 379. — H, Airy, Proceedings Royal Society, vol. XXI. p. 176. — ■ 
Beal, American Naturalist, 1873; vol. VII. p. 449.] 
^ [The term Phyllotaxis is used in works on descriptive botany to denote the mode of arrange- 
ment of leaves, and espetially of the foliage-leaves on the stem.] 
Fig. 144. — Apical region of a shoot of Coriaria -myrtifolia ; A in 
transverse section, B in lonifitudinai section; apex of the stem; bb 
leaves in pairs, i. e. in decussate whorls of twos ; k axillary bud ; 
youngest vessel. 
Fig 145.— Development of the flower of the mignonette (after Payer) '■> 
A a younger, B an older bud ; from the latter the anterior sepals s have 
been removed, the posterior ones left ; / / petals ; st stamens, the pos- 
terior ones already large, the anterior ones not yet even in a rudimentary 
state ; c the rudiment of the pistil. 
